It is really a good idea to make your show reservations on-line before your cruise starts. That way you won't be disappointed. Once aboard you can see if you can change things around if they have available seats. At least if you have a standing reservation you won't miss something due to a lack of seating. The downside of a ship with around 6000 passengers is that the show venues cannot handle the crowds without a reservation system. I know on our cruise aboard Allure in June, when we attended the water show there were very few open seats for walk-ups, and thus many people were disappointed. One guy caused a scene over it.
There will be more open seats for early shows on port days, for obvious reasons.
We loved all the shows. Very high standards and talent. Not your typical 'cruise ship salute to Hollywood revue' type of entertainment.